The present invention relates to a survey instrument, and in particular to a survey instrument, by which it is possible to accurately and easily align the center of a target with optical axis of a telescope of the survey instrument.
When measuring distance or surveying horizontal angle or vertical angle, optical axis of telescope of a survey instrument must be aligned with the center of a target. Accuracy of this aligning exerts influence on the distance measurement or measurement of horizontal angle or vertical angle.
In a conventional type survey instrument, when optical axis of telescope of a survey instrument is aligned with the center of a target, a surveyor collimates by means of a telescope, adjusts vertical angle adjusting mechanism of the telescope and horizontal direction adjusting mechanism of the telescope in order to align reticle of the telescope with the target to be measured. Further, at a position where the surveyor judged that these are aligned with each other, distance and angle are electronically read and the read value is displayed on a display unit.
In the conventional method as described above, aligning accuracy differs according to each surveyor, and this causes individual difference. Even when measured by the same surveyor, there are variations in alignment accuracy due to adjustment in each surveying. Further, when the target is at a long distance, it is often difficult to identify the center of the target. In adjusting the vertical angle adjusting mechanism and the horizontal direction adjusting mechanism, it is necessary to lock and unlock a locking device and to repeatedly perform fine adjustment, and this leads to complicated procedure and requires much time.